1. Field of the Invention
This invention relates to a light beam scanning device using a rotationally vibrating (hereinafter simply called "oscillating") deflector such as galvano-mirror.
2. Description of the Prior Art
For the representative types of the deflector which is generally used, there have so far been known a unidirectionally rotating deflector such as a rotary polygonal mirror and an oscillator deflector which swings back and forth like a galvano-mirror. While a relatively high scanning effect can be attained with the unidirectionally rotating deflector, the scanning operation is unavoidably interrupted in the oscillatory type deflector during return motion of the deflecting surface to is original position (this is called the backward or return rotation), because, with this type of deflector, only one direction of its rotation (this is called forward rotation) is usually employed. In this type of deflector, therefore, it is possible to improve its scanning effect by effectively utilizing not only its forward rotation, but also its backward rotation. On the basis of this concept, it has heretofore been known to effect the scanning operation in such a manner that, at both forward and return rotation of the deflector, a light beam is deflected by one and the same deflecting surface to make the deflecting direction of the light beam on the scanning surface to be mutually opposite between the forward and the backward rotations. However, since, in this scanning device, the scanning direction of the light beam on the scanning surface becomes opposite between the forward and the backward motion of the deflector, when this scanning device is utilized as a writing device, it becomes necessary to electrically reverse those informations to be written in for each line, which makes the device construction complicated. Further, in such device, when the scanning surface shifts at an equal speed, it is hardly possible to obtain scanning lines with equal space intervals.